Mud

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Mud is fine sand which is constantly or occasionally covered by water. It is formed by fine silt and clay deposited by the currents and tides. Mud will only settle where there is limited water movement as well as depression in the seabed. It can form vast plains of what seems to be an empty desert but in reality mud is very rich in nutrients and is able to support a great number of species.

Where is it found?

Muddy areas can be found in all areas from the deep sea to the shoreline, around the coast and seas of the UK. There are various classifications of mud habitats from deep sea to subtidal and intertidal. The intertidal area, exposed to both wind and sea, is often referred to as a mudflat.

Why is it important?

Looking at mud habitats at a surface level, perhaps with nothing but a few birds in a view, you could be mistaken for assuming that they are barren and lifeless habitats, but nothing could be further from the truth.

Deep sea mud occurs further down than sunlight is able to penetrate and where few plants are able to grow. However even in these dark depths wildlife thrives in muddy habitats. Burrowed in deep sea mud you can find species such as the bristleworm, while the muddy seafloor itself is home to species like brittlestars, spider crabs and lobsters.

In shallower areas below the point of the lowest tide (subtidal) there is also a great diversity of wildlife - including worms, bivalve shells, anemones and brittlestars, which feed on and inhabit the mud plains.

The species-carrying capacity is higher on sandier mud compared to soft mud. On soft mud species tend to grow quicker and become larger whereas higher numbers of smaller animals tend to occupy sandy mud habitats.

Intertidal mudflats are found in sheltered coastal inlets such as estuaries and harbours, around the coast of the UK, covering approximately 270,000 ha of land. Examples of species inhabiting mudflats are the shore crab, shrimps and sea snails, whilst buried in the mud itself is a vast number of worms, cockles and bivalves.

This understorey of wildlife provides a rich breeding and wintering site for waterfowl and wading birds, these can be found feeding on the flats doing low tide. In high tides fish will also use the habitat to forage.

Is it threatened?

Mud habitats are threatened by disturbance of currents, reducing the deposition of silt and clay while also carrying sediments away. Physical disturbance can be caused by dredging in shipping lanes and channels, as well as bait digging and oyster fisheries acting to alter the structure of the mud plains.

Mudflats are prone to pollution due to their proximity to the mainland. The result of pollution is often a reduction in benthic invertebrates and consequently on the species they support.

What are The Wildlife Trusts doing to help?

Following the assent of the Marine & Coastal Access Act, four regional projects were established to identify potential Marine Conservation Zones within England. The projects are stakeholder led and Wildlife Trust staff sit on all projects, at local, regional and a national level. These projects will ultimately put forward sites to protect special areas of the sea. Additional work on Marine Protected Areas is also underway in Wales and Scotland, whilst in Northern Ireland we are still campaigning for Marine legislation with a commitment to establishing these areas.

What can I do to help?

Visit wildlifetrusts.org/livingseas to find out how you can help our marine conservation work in the UK. Depending on where you live, local Wildlife Trust volunteers help out with everything from recording marine wildlife sightings to beach cleans and educational work. Visit our Living Seas pages online or contact your local Trust to find out more.